The present invention relates to a composition containing a fluoroelastomer such as vinylidene fluoridehexafluoropropene copolymers or vinylidene fluoridehexafluoropropene-tetrafluoroethylene terpolymers, and more particularly to a fluoroelastomer composition having an excellent scorching resistance, namely excellent processability and storage stability, and moreover having an excellent curability.
It is known that fluoroelastomers such as vinylidene fluoride-hexafluoropropene copolymers and vinylidene fluoride-hexafluoropropene-tetrafluoroethylene terpolymers can be cured, for instance, with a polyamine, as reported in Industrial and Engineering Chemistry, Vol. 49, 1687(1957). However, the polyamine has the drawback that it causes scorching during milling or molding processing.
In order to solve the problem on scorching, a study of a curing agent has been made. It is made clear at present that a carbamate compound such as hexamethylenediamine carbamate as disclosed in Rubber World, Vol. 37, 250(1957) or 4,4'-methylenebis(cyclohexylamine) carbamate as disclosed in Rubber Chemistry & Technology, Vol. 46, 619(1973) and a Schiff base such as N,N'-dicinnamylidene-1,6-hexamethylenediamine as disclosed in British Pat. No. 838,281 provide a fluoroelastomer composition having a scorching resistance. However, in case of hexamethylenediamine carbamate and 4,4'-methylenebis(cyclohexylamine) carbamate, the scorching resistance is still insufficient, and they have the drawbacks that curing takes place at the time of molding processing and consequently the mold flow is hindered in an early stage. On the other hand, in case of the Schiff bases such as N,N'-dicinnamylidene-1,6-hexamethylenediamine, curing at high temperatures is necessary, since the curing reactivity is low as compared with the carbamate curing agents, though the scorching resistance is sufficient. Moreover, the cured rubber has a high compression set. Also, N,N'-dicinnamylidene-1,6-hexamethylenediamine has a peculiar smell and gives out a foul smell at the time of roll milling or curing. Further, in case of using this curing agent, a tarry volatile material is produced in a cured rubber and it causes the cured rubber to stick a mold, so the surface gloss of the cured rubber is decreased with staining of the mold.
It is proposed in Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 78951/1977 to employ a curing agent such as hydrofluoric acid salt of hexamethylenediamine in order to eliminate the abovementioned drawbacks of the carbamate curing agent and the Schiff base curing agent, namely to provide a fluoroelastomer composition having a sufficient scorching resistance and an improved curability. The fluoroelastomer composition containing the proposed curing agent has a good scorching resistance as compared with the use of the above-mentioned carbamate curing agent, but is still insufficient in the scorching resistance in the storage under severe circumstances, e.g. at high temperature and high humidity.
It is a primary object of the present invention to provide a fluoroelastomer composition having a sufficient scorching resistance and an excellent curing reactivity.
This and other objects of the present invention will become apparent from the description hereinafter.